The present invention relates generally to devices and methods for restoring function to the spine. Specifically, the invention relates, to devices and methods for treating a damaged intervertebral disc while retaining the annulus fibrosis of the disc and, advantageously, stimulating tissue formation to restore function to the original disc structure.
Back pain affects millions of people and is a common cause of disability for the middle-aged working population. A frequent cause of back pain is rupture or degeneration of intervertebral discs. Intervertebral discs; located between the endplates or adjacent vertebrae, stabilize the spine, distribute forces between vertebrae, and cushion vertebral bodies. An intervertebral disc includes the annulus fibrosus, a structure that surrounds and confines an inner component, the nucleus pulposus. The annulus fibrosis is composed of a ring of collagen fibers and fibrocartilage embedded in a generally amorphous base substance. The nucleus pulposus is comprised of a mucoid material containing mainly glycoproteins and some collagen. In a healthy, undamaged spine, the annulus fibrosus prevents the nucleus pulposus from protruding outside the disc space and also resists torsional and bending forces applied to the disc.
Intervertebral discs may be displaced or damaged due to disease or aging. Disruption of the annulus fibrosus can allow the nucleus pulposus to protrude into the vertebral canal or intervertebral foramen, a condition known as a herniated or slipped disc. A rupture in the annulus fibrosis can allow the escape of nucleus pulposus components. The extruded nucleus pulposus may press on a spinal nerve, which may result in nerve damage, pain, numbness, muscle weakness and paralysis. Furthermore, as a disc dehydrates and hardens due to age or disease, the disc space height will be reduced, leading to instability of the spine, decreased mobility and pain. Moreover, excessive movement of the spinal segments caused by the disc space height reduction could weaken the annulus fibrosus and in certain cases, tear it.
Common methods of providing relief for damaged intervertebral discs include surgical removal of all or a portion of the intervertebral disc, followed by fusion of the adjacent vertebrae. Although fusion can eliminate the above symptoms, the restricted motion of the fused segment increases the range of motion required of the adjoining intervertebral discs and could enhance their degeneration.
Attempts at overcoming the problems with fusion include replacing the entire intervertebral disc with a mechanical, articulating intervertebral disc spacer. Many of these devices utilize multicomponent polymeric and metallic materials in an attempt to simulate the normal, healthy intervertebral disc motion. Such materials may disintegrate in the body and break down under repeated stressing over prolonged periods. Other attempts at overcoming the problems with replacing the entire intervertebral disc have included replacing the nucleus pulposus with elastomeric materials such as hydrogels.